This invention relates to a machining center for working relatively small workpieces each having a box shape, and more particularly, a machining center which is provided with a spindle head having vertical and horizontal spindles for working upper and side surfaces of a workpiece and in which tools are exchanged between the vertical and horizontal spindles and a tool magazine.
Most of conventional machining centers adapted to work the upper and side surfaces of workpieces are of a double column type and generally intended to work relatively large workpieces, whereas the upper and side surfaces of relatively small workpieces are worked by rotating a spindle head provided with one spindle. However, the working method of rotating the spindle head accompanies unstable restoring characteristic and lacks in rigidity, and thus, a time loss is involved for the working operation of a large workpiece to exchange tools and for a small workpiece, it is required to change the direction of the spindle head every time when tools are to be exchanged.